Tsunami generation and propagation from the Mjølnir asteroid impact

Abstract

In the late Jurassic period, about 142 million years ago, an asteroid hit the shallow paleo-Barents Sea, north of present-day Norway. The geological structure resulting from the impact is today known as the Mjølnir crater. The present work attempts to model the generation and the propagation of the tsunami from the Mjølnir impact. A multi-material hydrocode SOVA is used to model the impact and the early stages of tsunami generation, while models based on shallow-water theories are used to study the subsequent wave propagation in the paleo-Barents Sea. We apply several wave models of varying computational complexity. This includes both three-dimensional and radially symmetric weakly dispersive and nonlinear Boussinesq equations, as well as equations based on nonlinear ray theory. These tsunami models require a reconstruction of the bathymetry of the paleo- Barents Sea. The Mjølnir tsunami is characteristic of large bolides impacting in shallow sea; in this case the asteroid was about 1.6 km in diameter and the water depth was around 400 m. Contrary to earthquake- and slide-generated tsunamis, this tsunami featured crucial dispersive and nonlinear effects: a few minutes after the impact, the ocean surface was formed into an undular bore, which developed further into a train of solitary waves. Our simulations indicate wave amplitudes above 200 m, and during shoaling the waves break far from the coastlines in rather deep water. The tsunami induced strong bottom currents, in the range of 30-90 km/h, which presumably caused a strong reworking of bottom sediments with dramatic consequences for the marine environment.